1. Field of the Invention
This invention relates to a magnetic display system wherein the vertical position of light-absorptive magnetic particles and light-reflective non-magnetic particles is reversed in microcapsules to absorb or reflect incident light, thereby forming a contrast image of brightness and darkness therebetween.
2. Description of the Prior Art
As a first conventional technique concerning magnetic display systems, there is a magnetic display system in which a transparent plastic sheet is formed over the entire surface thereof with honeycomb-like cavities, each with a dimension of about 2 mm side and depth. Each cavity is filled with a white pigment liquid and magnetic particles and is sealed with a transparent sheet to prevent leakage of the filling matter. In this case, a rod-like permanent magnet is shifted over the entire display surface from one end of the back surface of the magnetic display to the other, thus bringing the magnetic particles in each honeycomb-like cavity toward the back side of the display plate and leaving a white color of the white pigment on the front surface. By moving a rod-like magnetic pen with its writing end in contact with the white surface of the display, the magnetic particles in the described area are brought to the front surface, thus forming an image.
A second magnetic display system utilizes a display in which microcapsules having sealed magnetic particles having anisotropy of shape are coated onto a non-magnetic substrate. A permanent magnet is a means to change the polarity orientation of the magnetic particles partially or totally, thereby forming and erasing images.
Furthermore, a third magnetic display system utilizes a display in which microcapsules having sealed magnetic particles and non-magnetic particles are coated and arranged on a substrate. A permanent magnet is a means for forming and erasing images by reversing the position of the magnetic particles and the non-magnetic particles in the microcapsules.
However, out of the above-described conventional magnetic display systems, in the first, an image is formed by a shift of magnetic particles in honeycomb-like cavities from the back surface to the front surface. Thus, it is impossible to obtain an image resolution sharper than the size of the honeycomb-like cavity, and it is technically difficult to make the size (breadth and depth) of each honeycomb cavity smaller than currently, on the order of a few millimeters. Further, it is not easy to perform the processes of molding for providing honeycomb-like cavities and of sealing the white pigment liquid and the magnetic particles, and it is almost technically impossible to make a display board providing honeycomb-like cavities have a size as large as a blackboard. Even if it is technically possible, high costs cannot be avoided. Further, such disadvantages are presented that it is technically extremely difficult to pour and seal the white pigment liquid and the magnetic particles into the honeycomb-like cavities provided over the entire surface having the above-described dimensions. Also, it is not easy to make the display have a size as small as pocket size, due to the construction noted above, and even if the display is made small in size, because of the fact that the honeycomb construction has a thickness of several millimeters, excessive weight for portable use cannot be avoided.
Furthermore, as compared with the display system in which the magnetic particles and the white pigment are sealed into the honeycomb-like cavities provided by plastic molding in the first conventional magnetic display system, the second is greatly advanced in that the quality of characters and images that can be formed is very superior, the polarity orientation of magnetic particles can be changed with a very slight magnetic flux, and further, a display having a desired size can be readily obtained. However, this system requires magnetic particles of nickel, or alloys thereof, capable of providing a surface gloss, having anisotropy of shape and having a flakier shape (i.e., a flat and elongated shape) than those of ferrite or iron oxide obtainable by mass production, as well as readily capable of polarization, because it is necessary to provide a strong contrast between light absorption when the particles are orientated vertically and light reflection when the particles are orientated horizontally. Disadvantageously, this leads to increased costs.
Next, according to the third conventional magnetic display system, the display is characterized by a construction in which the light-absorptive magnetic particles and the light-reflective non-magnetic particles are dispersed in an oily liquid, sealed into the microcapsules and coated on a substrate, and can offer the following numerous advantages as compared with the above-described first and second systems. As compared with the system in which the magnetic particles and the white pigment liquid are sealed into the honeycomb-like cavities provided on the substrate, microcapsules having minute particles diameters are utilized. Advantages are that side edge portions of characters and images that are formed can be made sharper. Amounts of the magnetic particles, non-magnetic particles and oily liquid for dispersion required for a given area of the display can be greatly decreased. A great cost reduction is possible as compared with the processes of molding the honeycomb-like cavities and of filling-sealing of the filling material. Possibilities in the selection of a rigid sheet, a soft and flexible film or the like for the substrate coated thereon with the microcapsules allow selections of various shapes of displays, such as a board type, a sheet type and a roll-scroll type. Selection of the display having a desired size can be made from mass produced sheets through cutting.
Furthermore, as compared with the prior art display systems in which the polarity orientation of the magnetic particles is inverted in the microcapsules, in the third prior art, advantages are that the magnetic particles used can be obtained at overwhelmingly .low costs, and the means for forming and erasing the characters and images can be greatly simplified.
As described above, as compared with the display systems cited as the first prior art system and the second prior art system, the third prior art system has many advantages. According to the present invention, this third prior art system is further improved so that, mainly, improvements in the quality of characters and images can be achieved.